The overall objectives of the proposed research is to determine the extent of hyperthermia and radiation-induced damage to the mammalian cell nuclear structure and function; and to determine the role of this damage in hyperthermia and radiation-induced chromosome aberration induction, cell inactivation and radiosensitization. With regard to the role of nuclear structure alterations in cell inactivation, we will determine the extent to which hyperthermia and radiation alters the structural and functional aspects of chromatin replication, including: DNA synthesis (replicon initiation, chain elongation and the ligation elongation of nascent DNA into parental DNA), synthesis of nuclear histones and matrix proteins, the processing of chromatin at the replication fork and the acquisition of higher order structure in replicating chromatin. A correlation will be made, in a synchronous S phase system, between the induction of any lesions in the replication of chromatin and both chromosome abrration induction and cell inactivation. Studies on the effect of hyperthermia and radiation on two additional nuclear phenomena (the structure of the nuclear envelope and the synthesis/processing of ribosomal RNA) will be initiated. With regard to radiation sensitivity, we will determine the role of chromatin structure(s) including replicating and transcriptionally active or ribosomal chromatin DNA, in the distribution of DNA thymine base damage and its repair. We will also determine the intranuclear distribution of selected DNA repair and replication enzymes, including Alpha and beta polymerase and the enzyme involved in the excission of thymine base damage, and determine the effect of hyperthermic exposure of the activity and distribution of these enzymes.